1. Field of the Invention
The present invention generally relates to an apparatus for controlling power generation performed in a generator of a vehicle based on electric power consumed by current consumers.
2. Description of Related Art
In recent years, to improve fuel economy of vehicles, an engine idle speed has been lowered as much as possible. Auxiliary units such as a generator, an alternator and the like are driven by an engine, so that the engine idle speed is changed with the driving torque required by the auxiliary units. For example, an alternator is driven to charge electric power to a battery. When a driving torque required by the alternator is increased, the engine idle speed is heightened. Therefore, the engine idle speed is often changed, and fuel economy of the vehicle undesirably deteriorates. To improve the fuel economy, for example, when a driving torque required by the alternator is increased in an idling time of an engine, power generation of the alternator is suppressed. Therefore, the increase of the driving torque required by the alternator is suppressed, so that the engine idle speed can be stabilized.
However, when current consumers of a vehicle consume a large amount of electric power of a battery charged by the alternator, the suppression of the power generation of the alternator causes an output voltage of the battery to be easily lowered. In addition, internal resistance of the battery sometimes becomes large due to degradation of the battery, or wiring resistance of wirings between the battery and each current consumer sometimes becomes large due to contact failures occurred in the wirings. In this case, the battery voltage applied to the current consumers is further lowered. When the battery voltage is extremely lowered, an engine controller consuming the electric power of the battery sometimes cannot control an engine. Therefore, there is a possibility that the engine cannot be reliably driven under control of the engine controller when a vehicle starts running.
Nowadays, current consumers assembled into a vehicle, such as an electrically operated power steering or the like, have been increased, so that electric power of a battery is intended to be consumed in large degrees. Therefore, when power generation of an alternator is suppressed, a battery voltage is often lowered. To solve this problem, an alternator controller is disclosed in Published Japanese Patent Second Publication No. 3283325. In this Publication, when a battery voltage is lowered to a value lower than a predetermined value due to the suppression of power generation of an alternator, the alternator controller controls the alternator to stop the suppression of the power generation and to generate electric power without being suppressed.
However, in a case where this controller is used in a vehicle, suppression and non-suppression of power generation in the power generation are often repeated in the alternator. As a result, an amount of the electric power generated in the alternator undesirably pulsates or fluctuates, so that the driving torque required in the alternator also pulsates or fluctuates. In this case, the engine idle speed inevitably becomes unstable. An engine controller sometimes controls an engine based on a driving torque required in the alternator. When a driving torque of the alternator pulsates, the engine controller cannot correctly detect the driving torque. Therefore, the engine controller cannot perform the optimum control for the engine due to pulsation of the driving torque.
Further, when the engine controller transmits a suppression instruction erroneously generated based on failures or the like to the alternator controller, the alternator controller erroneously controls the alternator to undesirably continue to suppress the power generation. In this case, a battery undesirably continues to discharge electric power. As a result, electric power of the battery is excessively lowered, and the battery is sometimes dead.
Moreover, a predetermined voltage value is preset in the controller, and the suppression of the power generation in the alternator is ended when a battery voltage is lowered to the predetermined voltage value. An operation voltage required to operate each current consumer differs from those required to operate the other current consumers. The predetermined voltage value is determined based on the highest operation voltage among those of the current consumers. In this case, even when only current consumers requiring operation voltages lower than the predetermined voltage value are operated, the suppression of the power generation is undesirably discontinued when the battery voltage reaches the predetermined voltage value higher than the operation voltages. Therefore, the increase of the driving torque required in the alternator cannot be sufficiently suppressed, and the fuel economy is lowered.